Fire presents many challenges, not least because of the variables that determine which suppression medium is appropriate for a given fire situation. Our goal on this two-part article is to provide guidance primarily based on a hazard-specific method and allow you to make an informed decision on appropriate fire-suppression measures, especially with regard to the processing and storage of flammable liquids.
Fire hazards are categorised as follows:
Class A – carbonaceous or flamable materials
Class B – flammable liquids
Class C – flammable gases
Class D – metals such as magnesium
Class F – fires typically associated with cooking similar to vegetable oils
Class E – electrical hazards.
As a producer of froth proportioners and firefighting displays, we specialise primarily in the Class B class: flammable liquids.
Foam is considered to be the simplest fire-extinguishing medium for both hydrocarbons and polar solvents. In addition, sure kinds of foam (known as wetting agents) are specifically for deep-seated Class A fires where water only could not penetrate the hearth load successfully.
Fire lessons.
How do we make foam?
Finished foam answer comprises a simple recipe of foam focus, water and air. Foam concentrate is usually mixed within the ratio of 1% or 3% to either 99% or 97% water.
Once the solution (premix) is created, it is pumped to the chosen discharge system – we will cover proportioning later in this article and discharge methods in Part 2. At this point air is entrained through the use of units designed to naturally aspirate the answer. The amount of aspiration and the type of concentrate determines the growth ratio. This is often break up between low, medium and excessive expansion. Low expansion is as much as 20:1, medium is 200:1 and excessive enlargement is more than 200:1. Only high-expansion foam may need the addition of a water-driven generator fan to increase the froth adequately, though naturally aspirated turbines are also used. The choice to decide on a selected growth ratio is decided by the hazard under review.
Put merely, water and oil do not combine. Applying only water to Class B products won’t suppress the burning vapours. This is a crucial level to make as it is the vapours, not the liquid itself, that burns. We need a medium that permits for the formation of a vapour-suppressing and oxygen-depleting blanket and/or a barrier film to be successful. Whatever technique is chosen to supply that blanket or movie, the objective is identical.
Steps of foam era Images equipped by Author / Contributor
A little of the history of froth improvement
We can date the event of modern foam concentrates from the 1960s onwards. Up to that point foam concentrates had been comprised of animal-based protein (typically floor hoof and horn is the base component). The primary disadvantage was because of restricted gas tolerance, which meant it was susceptible to fuel pick-up (mixing). A breakthrough got here with aqueous film-forming foams or AFFF’s. Instead of using protein as the base product, synthetic detergents gave foam a higher gas tolerance as properly as forming a vapour-sealing film throughout the floor of the fuel. Performance is further enhanced with the formation of a foam blanket when air aspirating gadgets are fitted.
Nevertheless, AFFF’s improvement did not utterly exchange the usage of protein-based foam. Fluoroprotein, or FP, meant that protein foam might both fight fuel pick-up (mixing) and supply a good resistance to warmth, outlined by the trade as ‘burn-back resistance’.
Further improvement in the 1980s took FP to the next level with film-forming fluoroprotein or FFFP. We now had one of the best of each worlds: a film-forming foam that also had good burn-back resistance.
The Nineteen Eighties further added to our record of acronyms with FFFP-AR – film-forming fluoroprotein, alcohol resistant. Alcohols or polar solvents had at all times presented a further problem as they had been water soluble and foam harmful. The FFFP-AR chemistry included a polymeric barrier, which protected the foam blanket from early destruction. The identical expertise also turned out there with the new technology of AFFF-ARs.
In latest years fluorine, one of the cornerstone elements to all foams, has turn out to be an environmental concern, because of persistence in groundwater. The industry has been presented with a serious challenge to remove the ‘fluoro’ component of all of the completely different foam focus sorts. We have witnessed an period of manufacturers’ claims and counter claims relating to the efficacy of a complete vary of newly formulated fluorine-free foam. The time period ‘SFFF’ (synthetic fluorine free foam) or ‘F3’ is used to define these foams, which have turn out to be the new normal and first choice for operators changing current inventory or reviewing new initiatives. As a foam proportioner manufacturer we must study the physical properties of froth fastidiously (especially viscosity) as they influence choices on the general proportioning answer. More of this later.
Multi-purpose foams such as the F3 alcohol-resistant varieties are increasingly important in the fuel-storage arena. The introduction of E10 petroleum, with its 10% ethanol-based biofuel content, signifies that the alcohol-resistant quality of SFFF/F3 is important to fight the small degree of water miscibility of the fuel.
All foam concentrate manufacturers will naturally promote their product as being extremely effective. The greatest method of comparing their claims is to familiarise your self with the empirically based mostly standard EN 1568 or UL162. The tests cowl extinction time, foam stability (via drainage time tests) and post-fire security (burn-back test). Hydrocarbons and the more demanding polar solvents are each included within the test protocols. This also covers fresh and seawater in addition to light and forceful software of the froth. Each foam is given a rating with IA being one of the best, IIID the worst. This means that you could problem foam suppliers so as to make an informed decision on the best foam in your needs.
Whilst EN 1568 is a superb benchmark standard, consciousness of the effects on foam efficiency from components outdoors the standard tests should be famous. For example, notably aggressive solvents can problem the firefighting effectiveness of certain foams. This may be exacerbated by completely different ambient air temperatures, the appliance technique, gasoline depth and so forth. Our advice can be to know the small print of the checks and try to match them to the foam’s appropriateness for your individual hazards. We would at all times advocate consulting particular person foam producers as they will typically provide particular in-house fire-performance information against a number of the extra uncommon fuels.
However, regardless of the froth manufacturers’ typically conflicting claims on performance, the earlier fundamentals of how foam is proportioned still stay: 1% & 3% concentrates are the norm for producing a finished foam.
Foams according to the expansion ratio Images provided by Author / Contributor
Critical components for success: the time and software rate matrix
Successful extinction of flammable liquid fires depends on two converging and complementary components: time and the speed at which completed foam is applied. Both are decided by empirically primarily based requirements published by our bodies such because the National Fire Protection Association (NFPA) within the United States and in Europe by the EN requirements.
The ‘time’ issue implies that for a given measurement of fire area it is necessary to use the foam for lengthy sufficient to achieve extinction and to forestall re-ignition. This is especially critical in guide intervention as firefighter’s will be at risk throughout post-fire operations. When it involves fastened safety for hydrocarbon and polar solvent tanks, the application time could be so lengthy as 60 minutes for the biggest tank diameters.
The software price refers to the amount of completed foam utilized per sq. metre. This varies in accordance with the gasoline and the foam kind however is presently at least four.zero litres per minute per sq. metre. One of the continued developments in foam performance is the chance that this shall be decreased, but standards typically take time to recognise product growth. Anything less than the minimum utility price implies that fire control is unlikely to be achieved. This means that firefighting sources, significantly in a manual hearth attack, have to be assembled before firefighting commences and this takes time. The advantage in becoming mounted methods is that the resources are already designed and built into the system for instant application.
Principle of foam extinguishment Images supplied by Author / Contributor
Foam proportioning methods: mixing water with foam concentrate
In order to permit readers to make an informed determination on how best to deal with their particular fire challenges, the following is an overview of the assorted foam proportioning strategies.
Foam inductors:
Typically associated with fire service deployment and restricted fastened methods functions. This makes use of the venturi precept to create a stress drop in a small aluminium or seawater material suitable gadget with built-in focus pick-up tube. The pressure drop created by the venturi draws the froth concentrate from a container the place it mixes with water to create foam answer. Both the pick-up tube and physique of the inductor are compact sufficient to be simply carried on a hearth equipment or fitted right into a pipework system.
However, whilst it’s considered to be the best methodology, it has severe drawbacks: (i) items are manufacturing unit calibrated so any changes to the hydraulics (caused by size of discharge line after the inductor, the elevation of the discharge device or a changing quantity of discharge devices) will probably require a system re-design; (ii) system design and sign-off are critical as deviations caused by pipe diameter modifications will adversely affect proportioning accuracy and potentially forestall any proportioning; (iii) adjustments in concentrate viscosity will undermine the flexibility of the venturi to draw concentrate into the downstream traces; (iv) strain loss is high, as a lot as 35%, so responsibility pump pressures need to be excessive enough to permit for it, potentially including additional cost into the system; (v) foam supply units need to be sized so as to not prohibit design flows; (vi) testing can’t be achieved with out creating premix and discharging completed foam. This will add to whole lifetime costs as a result of foam focus utilization, which needs to be changed, and the disposal of premix or foam.
Types of foam agentsImages equipped by Author / Contributor
Balanced stress proportioners:
These use an electrical or a combination of electric and diesel pumps to produce foam concentrate right into a proportioner at a higher stress than the incoming water-line strain. The proportioner is installed into the water line and regulates the mixing.
They are now related to older methods, where disadvantages embrace: (i) extra costs in hardware and design time; (ii) the foam pump is often restricted to a a lot tighter operating range, although the proportioner itself can accommodate wide ranges in flows; (iii) the froth pump wants an extra energy source, aside from water, so is not as reliably safe as a system with a potential single level of failure, such as a wholly water-driven system; (iv) typically, these techniques are very complex and cause high efforts at the buyer with set-up, commissioning and testing; (v) the recirculation of unused foam concentrate creates unnecessary agitation that has the potential to break the foam focus and entrain air, which in flip can undermine accurate foam proportioning and foam extinguishing effectiveness.
Bladder tanks:
Comprised of a steel strain vessel containing a versatile bladder (typically a butyl material) linked to a foam concentrate proportioner much like those fitted to balanced pressure proportioners. The incoming pressurised water compresses the foam filled bladder so that foam focus can be proportioned with water using the identical provide. The venturi principle is again brought into play because it creates a stress drop at the level of injection for the froth concentrate. Testing cannot be achieved without creating premix and discharging completed foam. This will add to entire lifetime prices because of foam concentrate usage, which needs to be replaced, and the disposal of premix or foam.
However, the bladder itself is seen as a weak spot as a result of nice care is required to avoid a broken bladder when commissioning a model new installation. It is rarely easy to work throughout the metal pressure vessel ought to problems occur, especially if and when a substitute bladder may be required: it all adds to the difficulty and price.
Compressed air foam (CAFS):
This isn’t a proportioning method within the typical sense as the foam is already proportioned using one of the previous methods. However, pressurised air is then added forcefully rather than naturally entrained or aspirated. As the title suggests, CAFS injects compressed air into the froth resolution at the point of discharge. The consensus view is that CAFS enhances the finished foam’s capability to cling to vertical surfaces permitting better penetration and cooling. This can be a profit in wildfire situations by coating susceptible structures to mitigate hearth progress. The restricted water provides related to distant wildfire areas signifies that the resource could be totally optimised. However, as with balanced strain proportioner foam pumps, an extra point of failure is possible as a end result of extra CAFS apparatus.
Water pushed or turbine foam proportioners:
FireDos have become synonymous with their distinctive water-driven foam proportioner. Now in its third era, the product is solely mechanical and highly reliable. A water-driven rotor supplies the driving force to drive a instantly coupled positive-displacement plunger or piston pump. This is provided with foam concentrate by way of an atmospheric foam tank adjoining to the FireDos unit. The proportioning pump is factory set to the required proportioning price and will proportion the froth concentrate precisely across a wide working range. The purely mechanical system provides cost-efficient and eco-friendly proportioning rate testing, utterly with out utilizing any foam focus or creating premix or firefighting foam.
FireDos GEN III foam proportioned. Images equipped by Author / Contributor
The benefits of FireDos Gen III FM accredited foam proportioners embody:
Reduced costs: proportioning fee is tested with out utilizing foam or creating premix or foam – cost efficient and eco-friendly.
Improved efficiency: constant proportioning price across a wide working range.
เกจ์แรงดัน of high-viscosity foam concentrates with improved suction capacity.
25% reduction in strain loss, in comparison with older generations, via hydraulic optimisation.
Improved cylinder cut-off for easy and fast adjustment to a unique proportioning rate.
FM permitted FireDos Gen III proportioners are so far the one FM approved water motor coupled variable proportioners utilizing FM approved flow meters. Using the take a look at return line this presents the possibility to examine the proportioning price throughout commissioning in addition to for annual tests, with out creating any premix, which is a really big profit for the person and relieves the environment.
In the second a half of this characteristic we will discover the consequences of viscosity on foam proportioning and typical foam application areas and beneficial discharge units.
For extra info, go to www.firedos.com
Written by
David Owen
Andreas Hulinsky
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